Gripping jaws for gripping sheet metal



April 18, 1967 s DOLNEY 3,314,270

GRIPPING JAWS FOR GRIPPING SHEET METAL Filed Oct. 2, 1964 4 Sheets-Sheet 2 April 8, 1967 s. M. DOLNEY 3,314,270

GRIPPING JAWS FOR GRIPPING SHEET METAL Filed Oct. 2, 1964 4 SheetsSheet 3 3% WIZIINZQENTOR.

0 gig ,Z@ ,4 TTOENEK April 18, 1967 Filed Oct. 2, 1964.

S. M. DOLNEY GRIPPING JAWS FOR GRIPPING SHEET METAL 4 Sheets-Sheet 4 INVE/VI'OF 5y WRQW/ United States Patent 3,314,270 GRIPPING JAWS FOR GRIPPING SHEET NIETAL Stanley M. Dolney, Parma, Ohio, assignor to The Cyril Bath Company, Cleveland, Ohio, a corporation of Ohio Filed Oct. 2, 1964, Ser. No. 400,997 14 Claims. (Cl. 72-305) This invention relates to gripping jaws for gripping opposite aligned faces of a margin of a sheet metal stock for exerting tension thereon for stretching the stock.

The invention is described herein as employed in stretch forming apparatus such as disclosed in the US. patent of Cyril I. Bath, No. 3,116,780, issued Ian. 7, 1964, and entitled, Prestretch Fixture and Combination Thereof With Drawing Die Press, its use in other types of apparatus being apparent from the illustrative example.

Heretofore, in stretch forming of sheet metal stock, the practice has been to grip two opposite end margins of a length of stock in suitable gripping heads and then to exert tension on the stock by moving the heads relatively apart from each other endwise of the stock while leaving the other margins unconfined. Difficulty had been experienced in obtaining a firm enough grip on the stock to prevent slippage of the gripped portion of the stock relative to the jaws of the heads in the direction in which the gripped margin is urged relative to the jaws by the tensioning forces, which direction is along the plane of the portion gripped between the jaws.

Theretofore those surfaces of the jaws which engage the opposite face portions of the stock have been roughened, generally by providing on each of the gripping faces of the jaws a multiplicity of very small diamond shaped pyramidal teeth distributed uniformly over the gripping area, and formed by crisscrossing two groups of grooves. However, after a certain amount of use, such teeth tend to wear down and round off, whereby their effectiveness is greatly reduced.

Next, attempts were made to provide jaws of which the gripping faces were serrated by parallel ridges of generally triangular cross section extending at right angles to the direction of tension on the portion of the stock gripped between the jaws. However, for the thicker steel sheets and newer alloys ever more heavy gripping jaw pressure was required, but as pressure increased, the sharp ridges on both gripping faces tended to embed deeply in the metal stock and act as shears. Often they cut partially through the metal, frequently so deeply that insufficient cross sectional area of stock remained for withstanding the tension applied. As a result, the weakened portions of the stock would tear apart before tension on the stock adequate for stretching was developed. Like difficulties occurred with very soft stock.

To overcome this difficulty, jaws of improved gripping qualities such as disclosed in the US. application of Stanley M. Dolney, Ser. No. 202,153, filed June 13, 1962, now Patent No. 3,253,448, and entitled, Gripping laws for Gripping Sheet Metal, was provided. These jaws were provided with gripping faces such that each face of the faces of a pair of companion jaws had a row of generally parallel elongated gripping ridges or teeth. In the plane of the gripped portion of the sheet stock, the ridges of each row were spaced laterally of their length from each other. Each ridge was oblique to the length of its row and to the direction of tension applied on that portion of the sheet stock gripped between the gripping faces. The ridges on one face extended, in the direction of their length, transversely of those of the other face, the obliquity of the ridges of one face being such that the ridges sloped from front to rear of the faces in a direction away from one lateral edge of the gripped sheet stock or pair "ice of faces. The obliquity of the ridges of the other face was such that they sloped from front to rear in a direction toward the same lateral edge of the gripped sheet stock. Thus the projected patterns of the ridges of the aligned faces of the jaws, in superposed relation on a plane parallel to the faces were a crisscross pattern when the jaws were in clamping position. Generally the angles to the tensioning direction made by the ridges of one face were equal in degrees to, but opposite to, those made by the ridges of the other face. These angles were 45 each, so that the projected crisscross pattern of the ridges was one in which the ridge of one face crossed those of the other face at and the direction of pull through the intersections of each crisscross bisecting the 90 angle thereof. This particular angle was desirable because the direction of shear of metal under tension applied in a given direction is about 45 to that direction, and hence a multiplicity of ridges extended substantially normal to the lines of shear of the metal sheet and accordingly assured a firm grip for resisting slippage.

laws with gripping surfaces have proven highly effective, especially with the newer alloys. However, with high speed production of articles or parts from sheet steel, such as used for automobile bodies, they had a disadvantage. This was due to the fact that the upper face of the lower jaw was thus provided with a rough surface or serrations. Ordinarily, in feeding sheet stock between a pair of open jaws, the sheet is fed edgewise, transversely of the direction of te-nsioning, so that the portion of the inserted end margin leading in the direction of insertion scraped across the ridges or serrations on the lower jaw while resting thereon and partially supporting the weight of the sheet. This was sometimes aggravated by pressure occasioned by waviness of the sheet as a result of which the upper crests of the waves bore again-st the upper jaw and forced the sheet even more firmly against the jaw surfaces. Thus the ridges acted as a file, teeth, or ridges, for removing burrs and scraping off small amounts of metal, foreign matter, and the like from the sheet surface. As a result, burr metal, filings and particles of foreign matter accumulated between the serrations and jaws and eventually were blown or carried by the sheets onto the surfaces of the dies. Often the accumulated material was such as to reduce the gripping effectiveness of the jaws. This problem is not pronounced, however, except in high speed production, but in the latter case it soon becomes an intolerable condition.

In accordance with the present invention, the jaws are modified over those heretofore described in two main respects. The lower, or gripping, surface of the upper jaw is provided with serrations forming gripping ridges. Beginning at the midp-ortion of the jaw, measuring in a direction transversely of the direction of tension, the ridges at one side of the midportion slope outwardly away from the midportion from front to rear of the jaw toward the adjacent later-a1 edge of the sheet. The ridges at the other side of the midportion slope outwardly from front to rear of the jaws toward the opposite lateral edge of the sheet. Thus the ridges at one side diverge from those at the other side in the direction from front to rear of the jaws. This has a distinct advantage in connection with the problem of necking in of a sheet laterally of the tensioning dimension, while the sheet is under tension, as hereinafter described.

Furthermore, it is preferable that the upper face of the lower jaw be smooth, that is, such as would result from ordinary machining, instead of being provided with serrations or ridges. One advantage of a smooth lower jaw is that it permits the sheet to slide more easily and accommodate itself to the jaws as they advance forwardly of the head during closure. Another advantage of a smooth lower jaw is that the sheet margin supported thereon during insertion of the sheet edgewise between the jaws can slide along the upper surface of the lower jaw without the lower jaw abrading the sheet surface appreciably or filing off burrs or loose material and the like, as would be the case were oblique ridges or teeth provided on the upper face of the lower jaw. This prevents the formation and accumulation of foreign particles of metal. If ridges are to be used for more limited production, they may be provided on both the upper jaw and the lower jaw. If provided, the serrations or ridges of the upper face of the lower jaw are aligned with and parallel to complementary ridges on the lower face of the upper jaw, so that the ridges do not form a crisscross pattern, as in the above identified application. On the contrary, both slope so as to assist in better cooperation of the sheet and jaws for accommodating themselves better to necking in of the sheets and thus preventing tearing the sheets transversely of the tensioning direction at the lateral margins immediately in front of, and adjacent to, the forward edge of the jaws.

Various other objects and advantages of the invention will become apparent from the following description, wherein reference is made to the drawings, in which FIGURE 1 is a diagrammatic front elevation of a press with a pair of stretch forming assemblages employing upper and lower gripping jaws of the present invention installed for operation;

FIG. 2 is a fragmentary front elevation of the stretch forming gripping head of the right hand assemblage illustrated on the line 22 of FIG. 1;

FIG. 3 is a vertical sectional view taken on the line 33 of FIG. 2;

FIG. 4 is a bottom plan view of the upper jaw taken on line 44 of FIG. 2, part of a sheet of stock being shown to illustrate the operating relation of the stock and jaw;

FIG. 5 is a top plan view of the upper jaw;

FIG. 6 is an enlarged sectional view taken on the line 66 in FIG. 5;

FIG. 7 is a top plan view of a metal sheet showing the pattern made by the ridges of the upper jaw on a plane parallel to the jaw faces;

FIG. 8 is an enlarged fragmentary view of a corner portion of the sheet of FIG. 7, illustrating in greater detail the cooperation of the jaws and sheet;

FIG. 9 is a side elevation of a set of jaws in which both the upper and lower jaws are serrated;

FIG. 10 is a bottom plan view of the upper jaw of FIG. 9;

FIG. 11 is a top plan view of the lower jaw of FIG. 9; and

FIG. 12 is a top plan view of both jaws in clamping relation to a fragment of a metal sheet.

Referring first to FIG. 1, the jaws are shown embodied in a stretch forming assemblage used in connection with the apparatus more fully described in the above identified application and patent wherein a sheet of stock is stretched generally horizontally. For brevity, the jaws are described herein in the operating position therein illustrated.

The assemblages are installed in a press 1 having a horizontal bed 2 and upright guides 3 which support a vertically reciprocal ram 4. A male drawing die 5 is installed on the bed in alignment with a complementary female drawing die 6 carried by the ram. The ram is moved upwardly and downwardly by piston and cylinder assemblages 7 including cylinders 8 in which pistons 9 are reciprocable, the pistons being connected by piston rods 10 to the ram for raising and lowering the ram.

For stretching the sheet preparatory to forming between the dies 5 and 6, two stretch forming assemblages 11 are provided on the bed. These assemblages are duplicates of each other and are arranged to engage opposite ends of the length of stock S for applying tension thereto independently of the drawing tension that might be imposed by the operation of the discs 5 and 6. Various means may be utilized for moving the jaws of the assemblages relatively away from each other for exerting the tension on the stock, but for purposes of illustration the means shown are those disclosed in the above patent. As there illustrated, each assemblage includes a gripping stretch head 12 mounted on a suitable carriage 13 which is arranged on a support 14 for movement endwise of the length of stock S. The support 14 is rigidly secured on the bed 2 and is provided with upwardly facing trackways 15 on which the carriage 13 may travel toward and away from the path of the dies 5 and 6. The carriage 13 is provided at its forward end with rollers 16 which ride on the trackways 15. At its opposite end, the carriage 13 is connected to one end of a link 17 by means of a pivot 18. The opposite end of the link 17 is connected by a pivot 19 to the support 14. Pivotally connected to the link intermediate the pivots 18 and 19, by means of a pivot 20, are piston rods 21 of pistons 22 which are operable in hydraulic cylinders 23. Controlled pressure fluid for stretching the stock is supplied to the cylinders by a suitable solenoid operated reversing valve 24 from a pump 25' driven by a motor 26. As described in the above application, the link 17 is practically coextensive in width with the length of the gripping head 12 in the direction transversely of the sheet stock. The head 12 is yieldably urged away from the dies by means of its piston and cylinder assemblages 'so as to exert tension on the stock, and is returned to starting position thereby.

For gripping the stock, each head 12 carries a pair of gripping jaws which extend the width of the piece of stock to be gripped and which have opposing aligned faces for engaging the opposite faces of the stock. In the form illustrated, the jaws are comprised of an upper jaw and a lower jaw 31. The jaw 30 is carried on a holder 32 and has a clamping face plate 33 fixedly secured to the jaw and facing dawnwardly. The plate 33 is at least coextensive with the width of the strip to be gripped. The jaw holder 32 is movably supported by suitable bolts 34 on a backup guide 35. The backup guide has a downwardly facing wedge cam surface 36 cooperable with an upwardly facing wedge surface 37 on the jaw holder 32. The bolts 34 secure the holder to the backup guide 35 for sliding movement forwardly and rearwardly along the wedge surfaces. The wedge surfaces 36 and 37 are arranged so that upon forward movement of the holder 32 toward the dies the upper jaw 30 is forced to move downwardly.

correspondingly, the lower jaw 31 comprises a holder 42 having a clamping face plate 43 fixedly secured thereto. The holder is secured by bolts 44 to a backup guide 45 for sliding along a wedge surface 46 thereon. The surface 46 cooperates with a complementary wedge surface 47 on the holder 42. The holders 32 and 42 may be thus constrained by keys 48 and 49, respectively, to lineal movement forwardly and rearwardly. It is apparent that with this arrangement forward movement of the jaws of a set moves their clamping surfaces, provided by the plates 33 and 43, toward each other and into wedged clamping engagement with the opposite face portions of the end margin of the stock S. Once a length of stock is gripped therebetween sufiiciently to exert any tension on the stock, further tension on the stock tends to pull the jaws forwardly toward the open end of the head, thereby increasing the wedge clamping engagement.

However, it is generally desirable that the jaws be moved forwardly for clamping pressure by suitable power means. For this purpose a row of piston and cylinder assemblages are provided. Each assemblage includes a cylinder 50 arranged in the head and accommodating a piston 51 having a rod 52 on the outer end. of which is a connector 53. The connectors engage in suitable recesses 54 and 55 in the plate holders. Pressure fluid is supplied through suitable reversible pressure lines 56 to opposite sides of the pistons 51 for advancing and retracting the jaws selectively. Pressure fluid is supplied to the cylinders 50 through a suitable reversing valve 58 from a pressure pump 59 driven by a motor 60. The structure thus far described is fully disclosed in the above application.

As mentioned, the gripping faces of the jaws with which the present invention is concerned, are provided on the plates 33 and 43. Referring to FIGS. 4 through 6, the top plate 33 has its bottom gripping face serrated with parallel spaced grooves to provide a plurality of parallel ridges 62 arranged side by side in a row and spaced laterally of their lengths from each other. The row extends transversely of the direction of tension applied on that portion of the stock gripped between the plates 33 and 43. Preferably, for ease in manufacture, the ridges are linear and are arranged closely adjacent to each other and are uniformly distributed along the row. They may be somewhat triangular in vertical cross section, but preferably have somewhat rounded peaks and valleys. The ridges are oblique relative to the direction of tension on that portion of the sheet gripped between the plates. The plate 33, as thus far described, is such as disclosed in the above identified application.

However, instead of all of the ridges of the plate 33 being parallel to each other, at least those at one end of the row diverge relative to those at the other end of the row in a direction from front to rear of the jaws. Preferably these divergencies are provided by making all ridges at each side of the center of the row, measuring transversely of the direction of tension in the plane of the gripping faces, parallel to the others on the same side,

with all ridges at one side of the center of the row diverging from front to rear of the jaws relative to all ridges at the other side of the center of the row.

Referring to the upper jaw in FIGS. 4-6, the plate 33 has ridges 62. The direction of tension in which the sheet S is urged to slip forwardly relative to the jaws by the applied tension is indicated by the arrow 63. Each of the ridges 62 extends endwise of its length, oblique to that direction, at an angle A, or at an angle B, as indicated in FIG. 5.

Preferably the angles A and B are 45 to the tensioning force. The 45 angles are preferred because of the tendency of metal stock under tension to shear along surfaces at an angle of 45 to the direction of tensioning forces. However, these angles may range from 75 to 45, or in some cases to 30.

The gripping face of the plate 43 of the lower jaw is preferably smooth and planar, such as would be provided by a simple planing operation. This arrangement assures that the margin of a sheet slid between the jaws transversely of the tensioning direction can slide easily without substantial abrasion and filing off of burrs and metal of the stock as in the case when the lower jaw is provided with ridges oblique to the tensioning direction.

It has been found that with clamping faces of this character, adequate tension can be applied to sheet stock without slippage of the jaws relative to the sheet and without appreciable weakening of the gripped portion of the sheet.

Referring next to FIGURES 7 and 8, a sheet held under tension above its elastic limit by the jaws, is illustrated diagrammatically. As there shown, when a sheet is thus tensioned by pulling on the jaws in the directions indicated by the arrows, with the lateral edges of the sheet unconfined, the lateral edges indicated at S tend to neck in from their outer original positions indicated at r to the new boundary, indicated at s. This necking in stresses the sheet adjacent the front of the jaws, tending to pull the material which was originally disposed along the forward edge of the jaws to a new position indicated by the line t, which is 90 to the necked in edge of the sheet, indicated by the line s. This tendency extends only a short distance from the lateral edge of the sheet toward the midportion of the row of ridges. If not relieved, it often causes tearing the the sheet from the lateral edge an inch or a few inches inwardly toward the mid-portion of the jaws.

However, with the ridges 62 divergent as described, as the stress increases, the resultant forces become more nearly parallel to the ridges 62. Consequently, there is a very slight flow or feeding out endwise of the ridges 62 of the metal gripped by the ridges at the margins of the stock. This slight flow prevents undue stress and thinning of the metal between the line t and the forward edge of the jaw, thus reducing tearing of sheets to a negligible number of them. This has a distinct advantage when compared to serrations which run at right angles to the direction of tension of a sheet. In such cases, the forward front serration tends to lock the metal and also to weaken the material on the straight line extending transversely of the sheet. Thus the metal cannot flow or feed out from between the jaws to any degree to relieve the tendency of the metal adjacent the front end of the jaws to move to the position indicated by the line t. Consequently, the metal often tears or splits, the tear taking substantially the shape defined by the forward edge of the jaw and the line t, in FIGURE 8. Inwardly of the sheet where the necking in has not accumulated to the degree at the lateral margins, the stress is much out of parallelism with the length of the sides. Consequently there is no feed out or flow such as near the edges.

While the ridges herein shown are of a linear pattern, they could be of curvilinear shape so long as the proper obliquity is retained. However, the endwise curvilinear shapes are much more difiicult to form and furthermore, such curves generally have components which are parallel to the direction of tens-ion, in which case the resistance to slippage is reduced. While it is preferred that the divergent relation of the ridges be provided from the midportion of the row to the ends, the critical portion is at the ends, which is where necking in is most severe. Consequently other surface configurations may be employed, beginning a few inches inwardly from the ends of the row.

The present jaw face structure is one that is particularly useful in connection with ordinary steels, but also can be used with the newer alloys which have an elastic limit and yield point considerably above that of the more conventional steels and the like. Their greatest advantage is in high speed production wherein very few metal particles, such as dislodged burrs and scrapings, from each sheet, soon accumulate to a very objectionable degree. The jaws and face plates lend themselves to ready manufacture.

Referring next to FIGS. 9 through 12, the jaws heretofore described may be provided with upper and lower face plates and 71, respectively. The upper plate 70 is identical with the upper plate 33, heretofore described, and has ridges 72. The lower plate 71 is also identical with the plate 70 and has ridges 73, but in operating position is rotated about a horizontal axis extending in the direction of tensioning force. As a result, the ridges 72 on the lower face of the upper plate diverge in the same direction as the ridges 73 on the upper face of the lower plate. Consequently, when viewed as in FIG. 12, the projected superposed patterns of the ridges on the two plates coincide. Thus the sheet is held firmly while at the same time provision is made for limited flow generally endwise of the ridges to eliminate tearing due to necking in at the lateral edges of the sheet.

Having thus described my invention, I claim:

1. In a stretch forming machine, gripping means for gripping one margin of a length of stock, a power driven stretch head for gripping the opposite margin, said head being movable relatively toward and away from said means for stretching the sheet along the dimension from said one gripped margin to the opposite gripped margin, whereby the margin of the stock gripped by the faces will be urged to slip in a forward direction relative to the head, a pair of clamping jaws mounted in the head, means on the head connecting the jaws thereto for movement to clamping and releasing positions, respectively, and for holding the jaws in fixed position relative to the associated head when the jaws are in clamping position, power means for moving the jaws into clamping position, said jaws having gripping faces, respectively, which are aligned in face to face spaced relation to each other when the jaws are in clamping position and which are elongated transversely of said forward direction, elongated gripping ridges on the gripping face of said upper jaw, said ridges being spaced from each other transversely of their length endwise of the face, at least those of the ridges adjacent the ends of the face being oblique to said forward direction, those ridges at one end of the face diverging in a direction from front to rear of the head relative to those at the other end of the face.

2. An apparatus according to claim 1 wherein the ridges at one end of the face are parallel to each other and the ridges at the other end of the face are parallel to each other, the ridges at said one end slope outwardly toward said one end from front to rear of the face and the ridges at said other end slope outwardly toward said other end from front to rear of the face.

3. An apparatus according to claim 2 wherein the acute angle of obliquity of the ridges at one end of the face is equal and opposite to the acute angle of obliquity at the other end of the face.

4. An apparatus according to claim 3 wherein the ridges are in a row which extends from said one end of the face to the other end of the face and the ridges at one side of the middle of the row diverge toward the end of the face adjacent said side and the ridges at the other side of the middle of the row diverge toward the end of the face adjacent said other side.

5. An apparatus according to claim 1 wherein the gripping face of the lower jaw is free from ridges.

6. An apparatus according to claim 1 wherein the gripping face of the lower jaw is smooth.

7. An apparatus according to claim 1 wherein the gripping face of the lower jaw has ridges complementary to those of the gripping face of the upper jaw, respectively, and each ridge of the lower jaw face is parallel to and aligned, normal to the jaw faces, with its complementary ridge on the upper jaw face.

8. A stretch head for gripping the margin of a sheet of stock for applying tension thereto along one dimension of the stock whereby the margin gripped by the head will be urged to slip forwardly relative to the head, said head comprising a support, a pair of clamping jaws mounted in the support, means on the support connecting the jaws thereto for movement to clamping and releasing positions, respectively, and for holding the jaws in fixed position relative to the support when the jaws are in clamping position, said jaws having gripping faces, respectively, which are aligned in face to face spaced relation to each other when the jaws are in clamping position and which are elongated transversely of said forward direction, elongated gripping ridges on the gripping face of said upper jaw, said ridges being spaced from each other transversely of their length endwise of the face, at least those of the ridges adjacent the ends of the face being oblique to said forward direction, those ridges at one end of the face diverging in a direction from front to rear of the support relative to those at the other end of the face.

9. An apparatus according to claim 8 wherein the ridges at one end of the face are parallel to each other and the ridges at the other end of the face are parallel to each other, the ridges at said one end slope outwardly toward said one end from front to rear of the face and the ridges at said other end slope outwardly toward said other end from front to rear of the face.

10. An apparatus according to claim 9 wherein the acute angle of obliquity of the ridges at one end of the face is equal and opposite to the acute angle of obliquity at the other end of the face.

11. An apparatus according to claim 10 wherein the ridges are in a row which extends from said one end of the face to the other end of the face and the ridges at one side of the middle of the row diverge toward the end of the face adjacent said side and the ridges at the other side of the middle of the row diverge toward the end of the face adjacent said other side.

12. An apparatus according to claim 8 wherein the gripping face of the lower jaw is free from ridges.

13. An apparatus according to claim 8 wherein the gripping face of the lower jaw is smooth.

14. An apparatus according to claim 8 wherein the gripping face of the lower jaw has ridges complementary to those of the gripping face of the upper jaw, respectively, and each ridge of the lower jaw face is parallel to and aligned, normal to the jaw faces, with its complementary ridge on the upper jaw face.

References Cited by the Examiner UNITED STATES PATENTS 3,065,781 11/1962 Muller 72302 3,241,352 3/1966 Lincourt 72-302 3,253,448 5/1966 Dolney 72305 CHARLES W. LANHAM, Primary Examiner.

L. A. LARSON, Assistant Examiner. 

1. IN A STRETCH FORMING MACHINE, GRIPPING MEANS FOR GRIPPING ONE MARGIN OF A LENGTH OF STOCK, A POWER DRIVEN STRETCH HEAD FOR GRIPPING THE OPPOSITE MARGIN, SAID HEAD BEING MOVABLE RELATIVELY TOWARD AND AWAY FROM SAID MEANS FOR STRETCHING THE SHEET ALONG THE DIMENSION FROM SAID ONE GRIPPED MARGIN TO THE OPPOSITE GRIPPED MARGIN, WHEREBY THE MARGIN OF THE STOCK GRIPPED BY THE FACES WILL BE URGED TO SLIP IN A FORWARD DIRECTION RELATIVE TO THE HEAD, A PAIR OF CLAMPING JAWS MOUNTED IN THE HEAD, MEANS ON THE HEAD CONNECTING THE JAWS THERETO FOR MOVEMENT TO CLAMPING AND RELEASING POSITIONS, RESPECTIVELY, AND FOR HOLDING THE JAWS IN FIXED POSITION RELATIVE TO THE ASSOCIATED HEAD WHEN THE JAWS ARE IN CLAMPING POSITION, POWER 